The present invention relates to a control system for an internal combustion engine having an air pump for controlling the engine in accordance with load.
In order to increase output power of the engine, there has been proposed a system in which a mechanical supercharger comprising an air pump is provided upstream or downstream of a throttle valve in an intake passage of the engine.
FIG. 4 shows a conventional system of an engine b having a supercharger a. The supercharger a is provided downstream of a throttle valve f in an intake passage e of the engine.
An air pump of the supercharger a is operatively connected to a crankshaft c of the engine b through an endless belt d running over a crank pulley and a pump pulley. The pump is driven by the crankshaft c at a predetermined step-down or step-up. A bypass h is provided around the supercharger a. The bypass h is provided with a control valve j. A rotating speed sensor g is provided on the supercharger a for detecting the rotating speed of the air pump. When the rotating speed reduces to a predetermined low speed, the sensor g produces a signal to open the control valve j. In a light engine load range, an opening degree of the throttle valve f is reduced and the control valve j is opened for returning discharged air to an inlet of the pump through the valve, thereby reducing the engine speed.
However, in such a light load state, the pumping loss of the engine b becomes large as shown by oblique lines in FIG. 5, particularly, even if the engine works as a pump at idling of the engine, so that fuel consumption increases at idling.
Japanese Patent Application Laid-Open 60-90924 and 60-209629 disclose systems each having an air pump for recovering the pumping loss of the engine.
The system of the former patent application has two pumps connected to the crankshaft of the engine. The output of the engine is controlled by the throttle valve. At light load condition of the engine, one of the pumps is operated in accordance with the pressure difference between the inlet side and the outlet side of the pump. The power generated by the pump is transmitted to the engine. At middle or heavy load condition, the other pump is operated by the engine to supercharge the air to the engine.
Since respective elements operate separately in dependency on engine operating conditions, the system is complicated in operation and construction.
In the system of the latter patent application, a variable delivery air pump is connected to the engine for controlling the power of the engine by varying the discharge of the pump. However, it is difficult to match the discharge of the pump with the opening degree of the throttle valve.
Japanese Patent Application Laid-Open 61-93232 discloses a system in which an air pump provided in the intake passage is driven by an engine through a continuously variable belt-drive automatic transmission.
However, since the intake air quantity passing through the throttle valve is small at light or middle engine load, the work for driving the air pump increases, resulting in a reduction of engine efficiency, although the pumping loss may reduce.